We are using sophisticated flow cytometric techniques to characterize, in detail, the B cell responses to HIV infection and to HIV vaccination. Our goal is to identify the antigen-specific B cells, isolate them, and then map the responses of the B cells to the viral proteins. Specifically, we use fluorescently-conjugated antigens (for example, the HIV envelope protein), to identify cells which bind those proteins. By using mutated forms of the antigens, we can selectively isolate cells which bind only certain regions of the protein of interest. We hope to use this to identify antibodies (and B cells producing them) that selectively bind important regions of the HIV envelope, such as the CD4-binding domain.